There's an article that can help troubleshoot similar issues to what you're experiencing. I'd go through each suggested step to see if that resolves the issue:
I tried to trouble shoot it with help from that page, and I still had the issue. It didn't help.
After I posted for some help last night, I found something that said to do CTRL+Shift to open iTunes in safe mode and that has been the only way to get any kind of playback and even with it there is still a slight delay which is ok with me.
I have the same problem. I purchased several episodes of a television program and they will not play either in iTunes or in Quicktime without stuttering, jerky video, choppy audio, and the video and audio being out of sync. As a new iTunes user, this experience has completely soured me and unless I find a solution.
I have absolutely no problem with playing video from any other source through any other player. I can stream videos fine from Amazon, YouTube, and everything in between, and videos downloaded from Amazon and elsewhere play just fine whether I'm using VLC, RealPlayer, or WMP. DVDs also play with absolutely no trouble whatsoever. It is only iTunes videos that have any trouble.
I have already consulted the page that was suggested here (and on other threads I've read), and nothing on that page was useful. (Troubleshooting iTunes for Windows Vista or Windows 7 video playback performance issues
This is extremely frustrating. I have Win7 Premium with 4 GB RAM and an AMD dual core 1.65 GHz processor. It may not be the ultimate gaming machine, but it's performed really well up until it encountered iTunes.
I also tried using QuickTime, thinking that might work better, so I downloaded the most up-to-date version, and playback was marginally better but still unwatchable.
Considering that this is paid content, it is unacceptable that it cannot be played on my computer -- and I have watched trailers for the episodes on YouTube (it's newly released), and they play perfectly, so I know it's not the episodes themselves.
Is there a codec that I should install? Is there any fix at all for this issue?
It seems that a large number of people experience this, which means that a lot of people are paying for something and then getting nothing -- and it's not a problem that can be discovered before the content is purchased. This is a very frustrating situation!